Only running on 4 cylinders? I think?

[jglimpse]

Ok so I have this 66 suburban with a V8. no idea what size. Sorry. So I got it running but it only seems to be running on 4 cyl, it is the even side the passenger side header gets hot when its running. I have checked the ignition every thing seems fine and all 8 cylinders are getting spark but after running say 5 min the manifold is still cold to the touch. it wont idle and when you try and rev it it is very slow to rev. I am planning to check the firing order tomorrow and other than that I have no idea what to do any help would be much appreciated. I will be more than happy to get anymore info if there is something you guys need Thanks alot